Many types of equipment gain added versatility from a flexible mounting arrangement. The most common example is a lamp which can be arranged to shine on an appropriate surface as needed. However, the kinds of arrangements used for lamps, which have a relatively heavy base and a relatively light superstructure are of limited utility for controlling the positioning of a relatively heavy superstructure on a relatively light base. Such an arrangement is needed, for example, for adjustable orientation video display terminals used in computer and communications systems.
Many arrangements have been used to allow video display terminals to be mounted so that the superstructure containing a cathode ray tube (CRT) can be tilted back and forth to minimize glare. When a superstructure is tilted so that its center of gravity is no longer directly above or below its support axis, gravity exerts a torque on the superstructure tending to change the tilt angle. A number of different arrangements are available to adjust and maintain a given tilt angle in a display terminal. For example, a display terminal sold by the Data General Corporation includes a costly high strength encompassing arm structure and a costly high strength housing to support the heavy CRT assembly from the sides. Here, the center of gravity is close to the support axis so that the forces tending to move the superstructure away from a given tilt angle are weak, and a relatively simple friction bolt will maintain a given tilt angle.
In another prior art display terminal sold by Teletype Corporation, a superstructure which is supported at the base has a tilt angle that is adjustable in steps over a relatively small range, up to 15 degrees from vertical. Here, the center of gravity of the superstructure is much higher than the support axis at the base, so that a large torque tends to move the superstructure away from a given tilt angle when the superstructure is in an extreme tilt position, because the center of gravity is then substantially displaced from a position above the support axis. The support includes a costly high strength toothed arrangement for locking the superstructure into one of seven positions.
Another base supported arrangement manufactured by Wyse Technology, San Jose, Calif., uses only friction to maintain a given tilt and also avoids the structural expense of the high strength support arms and the high strength superstructure housing. Here, the center of gravity is also much higher than the center of rotation of the superstructure, so that substantial forces tend to move the superstructure further from a neutral position when it is displaced substantially therefrom. However, the tilt is limited to 20 degrees from vertical, insufficient for support applications in which an operator sometimes works from a standing position. In this type of arrangement, if the friction is too great, the unit does not tilt readily; however, the friction must be great enough to maintain a superstructure position near the extreme levels of tilt adjustment.
Accordingly, there is no satisfactory mounting arrangement in the prior art for conveniently adjusting a heavy superstructure, such as the CRT assembly of a video display terminal, over a large continuously adjustable tilt angle. This large angle is needed, for example, if the operator using the terminal may be standing or sitting.